Liquid developers with uv curable additives and methods for their preparation

ABSTRACT

A method for printing a substrate by liquid developer electrography, the method comprising: (a) developing a latent image with liquid developer comprising toner particles dispersed in a carrier liquid, said toner particles comprising UV-curable additive; (b) transferring the developed image to the substrate; (c) at least partially fixing the image to the substrate; and (d) irradiating the at least partially fixed image with UV radiation to cure the UV-curable additive.

RELATED APPLICATIONS

This application derives priority from U.S. patent application Ser. No.11/524,019 and is a continuation in part of the above mentioned USpatent application and of International patent application No.PCT/US2005/026627, the disclosures of both of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to liquid developers for electrography, andparticularly to such developers that include UV-curable components.

BACKGROUND OF THE INVENTION

In many printing systems, it is common practice to develop a hardcopy ofan image using a photoconductive surface. The photoconductive surface isselectively charged with a latent electrostatic image having image andbackground areas. A liquid developer comprising charged toner particlesin a carrier liquid is brought into contact with the selectively chargedphotoconductive surface. The charged toner particles adhere to the imageareas of the latent image while the background areas remain clean. Ahardcopy material (e.g. paper) is brought, directly or indirectly, intocontact with the photo-conductive surface in order to transfer thelatent image. Variations of this method utilize different ways forforming the electrostatic latent image on a photoreceptor or on adielectric material.

Typically the liquid developer (also referred to in the art as liquidtoner) comprises a thermoplastic resin (polymer) as the basis for thetoner particles (also referred to in the art as ink particles), and anon-polar liquid as a carrier liquid in which the toner particles aredispersed. Generally, the toner particles contain a colorant such as apigment.

U.S. Pat. No. 5,212,526 describes a method and device for simultaneouslytransferring and fusing an image from an image receptor to a recordingmedium. The method includes forming a toned image layer on a surface ofan image receptor, the toned image layer comprising a toner material anda radiation curable material. The toner may be dry or liquid.

U.S. Pat. No. 6,837,839 describes a method for printing an image on apage by an electrophotography process comprising transferring a tonerimage to a page, and separately fusing the toner to the page by applyingUV light to the toner. The toner is especially formulated to facilitatecuring and/or fusing of the toner to paper. It is mentioned that thetoner may include toner particles suspended in a UV curable resin.

JP 61-156262 describes a liquid developer for electrostatic photographyhaving toner particles that comprise a coloring agent and a copolymer ofmono-functional and multi-functional (meth)acrylates. Themulti-functional (meth)acrylates mentioned, have between 2 and 4functional groups. The reference states that suitable proportions ofmulti-functional (meth)acrylates to mono-functional (meth)acrylates arein the range of about 0.01-1:1 (by weight).

SUMMARY OF THE INVENTION

An aspect of some embodiments of the invention relates to a method forprinting an image with a liquid developer having a UV-curable additivein the toner particles. The method includes at least partially fixing animage to a substrate, for example paper, and then curing the UV-curableadditive. In some embodiments, the UV-curing is carried out in-line, atthe speed of the printing process. Optionally, the irradiation is withina minute or less, optionally 10 seconds or less, after the image istransferred to the substrate.

In some cases, images printed by a method according to embodiments ofthe invention were found to exhibit improved abrasion and/or peelingresistance.

Another aspect of some embodiments of the invention, relates to a methodfor printing an image with a liquid developer having a UV-curableadditive in the toner particles, wherein the UV-curable additivecomprises multi-functional acrylates. Optionally, the carrier liquid isfree of multi-functional acrylates.

A preferred embodiment of the invention embodies the two above-mentionedaspects, and includes at least partially fixing an image to a substrate,the image comprises toner particles with a multi-functional acrylate asa UV-curable additive, and then curing the additive.

In the context of the present invention, a multi-functional acrylate isan acrylate with 4-6 or more functional groups, preferably 6 functionalgroups. Optionally, the toner particles are substantially free ofmono-functional acrylates, since they are less reactive thanmulti-functional ones. In this context, substantially free means thatmono-functional acrylates make less than 10%, optionally less than 1% ofthe acrylates in the toner particles.

An aspect of some embodiments of the invention concerns compositions ofliquid developers having a multi-functional acrylate as a UV-curableadditive in the toner particle and/or in the carrier liquid. In thetoner particles polyester acrylates are preferred, while in the carrierliquid polyurethane acrylates are preferred. Methacrylates are notsuitable for replacing the above-mentioned acrylates as they were foundto cure too slowly.

The UV curable additives preferably have good wetting properties towardsthe pigment. Good wetting properties mean that they physically attach topigment surface allowing high degree of dispersability and good grindingconditions. Some examples of UV curable additives with generally goodpigment-wetting properties are multi-functional urethane acrylates andmulti-functional polyester acrylates.

In a first exemplary embodiment, the UV-curable additives areincorporated in the toner particles, and are selected fromhexa-functional acrylates, multi-functional polyester acrylates andmulti-functional polyurethane acrylates.

Preferably, a stabilizer is added to the composition of the tonerparticles to inhibit any initiation of curing in the absence of strongUV irradiation. Strong UV irradiation is, for instance, between about200 and about 400 mJ/cm² (to be measured on top of the printed surface).As UV-curing is many times initiated by free radicals, the stabilizeroptionally comprises a free radical scavenger.

In a second exemplary embodiment, the UV-curable additives are presentin the carrier liquid.

In a third embodiment, UV-curable additives present in both the tonerparticles and in the carrier liquid.

Optionally, photo initiators are included in the composition of theliquid developer. A photo-initiator is a compound that, when irradiatedwith light, readily produces free radicals that initiate the curingprocess. Preferably, the wavelength at which UV irradiation is appliedfor curing and the wavelength at which the photo-initiators produce freeradicals are selected to match each other.

Preferably, the photo initiator is added after grinding, for instance,to the liquid carrier. Adding the photo initiator in the grinding stagemight cause, with some initiators, premature initiation of apolymerization reaction by heat that develops during grinding. When thetoner particles are dispersed in the liquid carrier, some of theinitiator migrates to the toner particles, or attached to them, so uponUV irradiation, the photo initiator put into the carrier can initiate areaction of the UV-curable additive, put into the toner particle.

In the above-mentioned second embodiment, it is preferred to includeacrylates of lower functionality (that is, mono-acrylates orbi-acrylates) in the liquid carrier, as they are useful to enhance theincorporation of the UV-curable additives and/or of the photo-initiatorsinto the liquid carrier. Bi-acrylates are preferred, as they were foundto be more reactive than mono-acrylates. Optionally, the ratio betweenmulti-functional acrylates and acrylates of lower functionality ispreferably from 1:5 to 1:20, more preferably from 1:8 to 1:12.

Without being bound to theory, it is suggested that the lower acrylatesare useful because of their lower viscosity on one hand, andcompatibility with the higher acrylates, on the other hand. Lowerviscosity, in this context, is about 30 cps or lower at roomtemperature. In this application room temperature is about 25° C.

The following are examples of some powder photo initiators which can bedissolved in low viscosity acrylates and be used in embodiments of thepresent invention: Irgacure 369, 651, 184, 1300, 819, Darocur TPO—allfrom Ciba, and Additol EPD. All the above-mentioned are manufacture byCiba, except for the last one, which is manufactured by Cytec (formerlyUCB).

Another aspect of some embodiments of the present invention is a methodof making toner particles with a UV-curable additive, the methodcomprising grinding a pigment with a thermoplastic resin and theUV-curable additive. The UV curable additive comprises at least 75%multi-functional acrylates. Hexa-functional acrylates are preferred, andso are polyester acrylates. Optionally, the pigment, thermoplasticresin, and UV-curable additive are ground together with otheringredients known in the art to be incorporated in a toner particleduring grinding, such as a charge adjuvant. The grinding is in thepresence of a liquid, optionally the liquid is the liquid carrier, forinstance, Isopar®.

Another aspect of some embodiments of the present invention is aone-phase liquid carrier for liquid toner particles, comprising anon-polar liquid and multi-functional acrylates. In an embodiment of theinvention, the multi-functional acrylates constitute about 0.05% toabout 0.5% (w/w) of the liquid carrier. Preferably, the UV curableadditive in the carrier liquid has an evaporation rate substantiallysmaller than that of some other liquid components of the carrier liquid,and the developed image is heated before being irradiated with UV, suchthat evaporation of the more volatile liquid components of the carrierliquid takes place. In this way, the concentration of the UV-curableadditive in the image is increased to a concentration at which effectivecuring can take place. A carrier liquid with low concentration ofUV-curable additives which are less volatile than other liquidcomponents of the carrier liquid may give excellent results also withUV-curable additives different than those described herein, forinstance, with the additives described in copending U.S. patentapplication Ser. No. 11/524,019 and International patent application No.PCT/US2005/026627.

As the multi-functional acrylates are insoluble with many non-polarliquids, and in particular in ISOPAR®-L, which is often used as a mainconstituent of liquid developers, providing such a one-phase liquidcarrier requires a unique preparation method.

Thus, another aspect of some embodiments of the present invention is amethod for preparing a one-phase liquid carrier comprising a non-polarliquid and a multi-functional acrylate. In this context, the one phaseis determined by visual examination, that is, a liquid carrier thatlooks clear is considered one-phase. The method comprises preparation ofa mixture of multi-functional acrylates mixed with—and optionallydissolved in acrylates of lower functionality to obtain an acrylatemixture, and then diluting this mixture with the non-polar liquid.Preferably, the dilution is made in two stages: first, the acrylatemixture is diluted with a first quantity of non-polar liquid and mixedin a high shear mixer to obtain a concentrated carrier, and then, theconcentrated carrier is diluted to final concentration of acrylates,optionally, with regular stirring. In the obtained developer, theacrylate concentration is about 2% (w/w of the carrier liquid),generally between 0.5% and 5%. In some embodiments, bout 10% of theacrylates in the liquid carrier are multi-functional acrylates.

Thus, an aspect of some embodiments of the present invention relates toa method for printing a substrate by liquid developer electrography, themethod comprising:

(a) developing a latent image with liquid developer comprising tonerparticles dispersed in a carrier liquid, said toner particles comprisingUV-curable additive;

(b) transferring the developed image to the substrate;

(c) at least partially fixing the image to the substrate; and

(d) irradiating the at least partially fixed image with UV radiation tocure the UV-Curable additive.

Another aspect of some embodiments of the present invention relates to amethod for printing a substrate by liquid developer electrography, themethod comprising:

(a) developing a latent image with liquid developer comprising tonerparticles dispersed in a carrier liquid, said toner particles comprisingas a UV-curable additive a substance selected from: a hexa-functionalacrylate or a multi-functional polyester acrylate;

(b) transferring the developed image to the substrate; and

(c) irradiating the image with UV radiation to cure the UV-Curableadditive. Optionally, before irradiating the image in (c) the image isat least partially fixed to the substrate.

An aspect of some embodiments of the present invention relates to amethod for printing a substrate by liquid developer electrography, themethod comprising:

(a) developing a latent image with liquid developer comprising tonerparticles dispersed in a carrier liquid, said carrier liquid comprisinga multi-functional acrylate as a UV-curable additive;

(b) transferring the developed image to the substrate; and

(c) irradiating the image with UV radiation to cure the UV-Curableadditive. Optionally, before irradiating the image in (c) the image isat least partially fixed to the substrate.

In exemplary embodiments of the invention, the carrier liquid and thetoner particles comprise UV curable additives. Preferably, the UVcurable additive is present in a percentage of 0.5% to 5% by weight ofthe carrier liquid.

In a preferred embodiment of the present invention, the UV curableadditive in the carrier liquid has an evaporation rate substantiallyless than that of at least some other liquid components of the carrierliquid and after the developing and prior to the irradiating a portionof the other liquid components is evaporated, such that theconcentration of UV curable additive is increased by an amount such thatUV irradiation is effective to cure the curable additive.

Optionally, the fixing of the image to the substrate includesirradiating the image with IR radiation. Alternatively or additionally,the fixing includes heating the image and the substrate. Alternativelyor additionally said fixing includes pressing the image against thesubstrate utilizing a heated member.

Optionally, in embodiments of the invention, transferring comprises:

first transferring the developed image to an intermediate transfermember on which the image is heated; and

transferring the heated image to a final substrate by pressing theheated image against the final substrate.

In exemplary embodiments of the invention, the image is at least partlyfused to the substrate prior to being irradiated with UV irradiation.

Optionally, the UV irradiating is carried out within 10 seconds of thetransfer to the substrate.

In preferred embodiments of the invention the UV-curable additivecomprises a multi-functional acrylate.

An aspect of some embodiments of the invention concerns a method formaking toner particles, the method comprising grinding together amixture comprising a thermoplastic resin swelled with an aliphaticliquid (which optionally is isoparaphinic), a pigment, and a UV-curableadditive. Preferably, the UV-curable additive comprises multi-functionalacrylate.

An aspect of some embodiments of the invention concerns a method formaking a liquid developer, the method comprising making toner particlesin a method according to embodiments of the invention, and dispersingthe toner particles in a liquid carrier. Optionally, the aliphaticliquid is the same as the liquid carrier. Optionally, the methodcomprising mixing a photo-initiator with an acrylate of lowerfunctionality, and adding the obtained mixture to the liquid carrier.Optionally, thermoplastic resin is a copolymer of ethylene with acrylicor methacrylic acid.

An aspect of some embodiments of the present invention concerns a methodof making a one-phase liquid carrier comprising a non-polar liquid and amulti-functional acrylate, the method comprising:

(a) mixing the multi-functional acrylate with acrylates of lowerfunctionality to obtain an acrylate mixture, and

(b) diluting the obtained mixture with the non-polar liquid, optionallyto a concentration of 0.5-5% acrylates in the liquid carrier.

In exemplary embodiments, (b) comprises:

(b.1) mixing in a high shear mixer the acrylate mixture with a firstquantity of non-polar liquid to obtain a concentrated carrier; and

(b.2) diluting the concentrated carrier with a second quantity ofnon-polar liquid.

Optionally, the non-polar liquid is an isoparaphinic liquid.

Optionally, the diluting is

Preferably, the multi-functional acrylate is tetra-functional,penta-functional, or hexa-functional. In some embodiments,hexa-functional acrylates are preferred.

Optionally, the multi-functional acrylate is a polyester acrylate;alternatively or additionally, it is a polyurethane acrylate.

An aspect of some embodiments of the invention concerns a one phaseliquid carrier comprising multi-functional acrylates, optionallypolyurethane acrylate, alternatively or additionally, a hexa-functionalacrylate. Optionally, the one phase liquid carrier further comprisesacrylates of lower functionality, preferably bi-functional acrylates.

In exemplary embodiments of the invention, the multi-functionalacrylates together with the acrylates of lower functionality form from0.5% to 5% of the liquid carrier. Preferably, the ratio betweenmulti-functional acrylates and acrylates of lower functionality is from1:5 to 1:20.

Some embodiments of the invention relate to a liquid developercomprising toner particles dispersed in a liquid carrier, the liquidcarrier being according to any embodiment of the invention.

An aspect of some embodiments of the invention concerns a liquiddeveloper comprising toner particles dispersed in a liquid carrier,wherein the toner particles include a thermoplastic resin, a pigment,and a UV-curable additive selected from: a hexa-functional acrylate, amulti-functional polyurethane acrylate or a multi-functional polyesteracrylate. Preferably, the UV-curable additive wets the pigment. Inexemplary embodiments, the UV-curable additive comprises a polyesteracrylate. Optionally, the UV-curable additive comprises ahexa-functional polyester acrylate and/or other hexa-functionalacrylates- and/or tetra-functional acrylates. Optionally, the UV-curableadditive makes 0.5 to 5% of the non-volatile solids in the tonerparticles.

In exemplary embodiments, the liquid carrier comprises photo-initiatorsand an acrylate of lower functionality, preferably, a bi-functionalacrylate. Optionally, the acrylate of lower functionality has at roomtemperature a viscosity of up to 30 cps.

Optionally, the thermoplastic resin comprises a copolymer of ethylenewith acrylic or methacrylic acid.

Optionally, the toner particles in developers or methods according toembodiments of the invention are tentacular.

Optionally the liquid carrier of the developer according to theinvention is a liquid carrier according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

In order to better understand the invention and to see how it may becarried out in practice, some embodiments will be described below asnon-limiting examples only, with the assistance of the Figures, wherein

FIG. 1 is a flow chart of a method for preparing toner particlesaccording to an embodiment of the invention;

FIG. 2 is a schematic illustration of a printing machine having a UVsource, for in-line UV curing;

FIG. 3 is a flow chart of a method for dissolving a multi-functionalacrylate in non-polar liquids according to an embodiment of theinvention; and

FIG. 4 is a flow chart of one of the steps in the method of FIG. 3,according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Liquid developers that had UV curable additives in the toner particlesas described below had a higher abrasion resistance than that obtainedwith the same developers but without the UV curable additives. Thedifference was of 20 units using BVS™ paper by Papierfabrik Scheufelen.BVS paper is an acrylic coated paper. Units for measuring abrasion aredescribed below.

Liquid developers that had UV curable additives in the liquid carrier asdescribed below had peeling resistance 100% higher than that obtainedwith the same developers but without the UV curable additives. Themeasurements were on uncoated paper (Hadar-Top™ by Hadera Paper,Israel.) Explanation of peeling resistance measurement is providedbelow.

In the following, described are the preparation of the toner particlesand the liquid developer, the printing process, and the printingapparatus used by the inventors in the development of the presentinvention.

Preparing Toner Particles and Liquid Developer

FIG. 1 is a flow chart of a method (100) for preparing a liquiddeveloper with UV-curable additives according to an embodiment of theinvention. This UV developer is referred herein as UV1.

Production of Toner Particles

First, 600 grams of polyethylene-acrylic acid co-polymers (Nucrel 699,DuPont) and 150 grams and ACE5120, DuPont is mixed in a Ross doubleplanetary mixer with 1750 grams of Isopar L (an iso-parafinic oilmanufactured by EXXON) carrier liquid at a speed of 60 rpm and atemperature of 130° C. for one hour (102). During this heating the resinsolvates carrier liquid and is swelled. The temperature is then reducedand mixing is continued until the mixture reaches room temperature. Theend result is a homogeneous paste.

Next (104) 1240 g of the paste prepared in 102 are charged into a UnionProcess 1 S ball attritor together with 55.6 g Toyo Lionel Blue pigment,4.14 g Heliogen Green pigment, 9.2 g aluminum di-stearate as chargeadjuvant and 18.4 g of hexacrylate ebecryl 450 UV-curable additives and18 mg of NPAL by Albermale as UV-stabilizer. The mixture is ground at58° C. for 1.5 hours, at 250 rpm, followed by additional grinding at 40°C. for 10.5 hours at 250 rpm to obtain toner particles dispersed inliquid carrier. The toner particles obtained by this process aretentacular.

The percentage of polymer is optionally about 85% (80%-90%), thepercentage of aluminum tri-stearate is about 2%, (1%-3%), the percentageof UV-curable additive is about 2% (1%-3%), and the percentage ofpigment is about 13% (10%-20%) all by weight of the NVS. The amounts inparentheses are preferred, but not limiting ranges of each of thecomponent materials.

In practice, toner compositions can vary depending on thecharacteristics, color, etc. desired, so that in some situations thepercentages can vary within (or even outside) the ranges given inparentheses after each percentage component. In addition, the type ofpolymer used and other components can vary, as known in the art.

The dispersed toner particles in the liquid carrier are chargedutilizing 30 (5-40) mg solids of charge director per g toner solids.Also added is a photoinitiator mixture, in an amount of 0.2% (0.1-0.4)of the liquids in the formulation.

The photoinitiator mixture is prepared by mixing 90 grams of DPGDA(Dipropylene Glycol Diacrylate by UCB) with 10 g of a 1:1 mixture of TPOand Darcur 1173 (two photoinitiators by Ciba (Darocur 1173 is2-Hydroxy-2-methyl-1-phenyl-propan-1-one, and TPO isdiphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) for half an hour at 60rpm using simple magnetic stirrer at 50° C.

The charged toner particles with the photoinitator mixture are diluted(106) with additional Isopar L and Marcol 82 (EXXON) to produce a tonerhaving a 2% NVS, with 98% (optionally 97%-100%) of the carrier liquidbeing Isopar L and 2% (optionally 0-3%) Marcol 82. A commerciallyavailable charge director (HP Indigo Imaging Agent 4.0) was used in theexperiments. Other charge directors as known in the art can also beused.

The result is a cyan toner. All of the experiments reported below werewith cyan toner, although the inventive concepts can be applied to othercolor toners, for which different pigments would be used, as well.

Other suitable UV-curable additives include: Ebectryl 812,(tetrafunctional functional polyester acrylates by UCB), IRR 182,Ebecryl 450, Ebecryl 860 and Ebecryl 3201, all by UCB, and CN9006(hexa-functional urethane acrylate), CN 2200 (polyester acrylateoilgomer), CN 2902 (aromatic urethane acrylate), and CN 2100 (aminemodified epoxy acrylate). Ebecryl products are by UCB, and CN productsare by Sartomer.

It should be understood that different pigments may be better wetted byother UV-curable additives.

The Printing Process

In printing experiments, latent image was developed with theabove-described developers, transferred to paper, fixed, and thenirradiated with UV. Such a process may be carried out with any knownmethods for forming latent image, developing latent images, transferringdeveloped images to substrates, and fixing the image to the substrate.In the experiments described below, a HP 5000 Press was used.

Fixing is preferably carried out by heat and pressure, for example,during transfer of the image from a heated intermediate transfer memberunder pressure. In some embodiments of the invention curing may beobtained fast enough to be carried out in-line, at the speed of theprinting process. A printer 200, with UV-lamp suitable for such in-linecuring is schematically shown in FIG. 2. The printer includes aphotoreceptor 202 charged by a charger 217, on which a laser (204)creates a latent image comprising pixels charged at to differentvoltages. This latent image is developed by a developer or toner appliedby a developer apparatus (206), which can be of any form known in theart. The developed image is transferred to an intermediate transfermember (ITM) 208, which transfers the image to a substrate 210, such aspaper. During the transfer to the substrate, the image is pressedbetween heated ITM (208) and a pressure cylinder (212), and continuesmoving towards a UV lamp (214), which cures the UV-curable additive toprovide an image with improved rub-resistance and peeling resistance.The printer 200 also includes a cleaning station 216 of any type knownin the art for cleaning the photoreceptor. Optionally, it also includesa cleaning station 218 to remove residual toner from the ITM. In someembodiments of the invention the image is at least partially fixed andfused during transfer to the substrate, by heat and pressure.

FIG. 3 is a flow chart of a method (300) for incorporatingmulti-functional acrylates into a non-polar liquid according to anembodiment of the invention. The method (300) comprises mixing (302)multi-functional acrylates with acrylates of lower functionality toobtain an acrylate mixture, and then diluting (304) this mixture withthe non-polar liquid. Preferably, the dilution (304) is made in twostages, as illustrated in FIG. 4: first, a quantity of non-polar liquidis added (402) to the mixture; then mixed (404) in a high shear mixer toobtain a concentrated carrier, and then, a second quantity of non-polarliquid is added (406) to the concentrated carrier as to obtain a finalconcentration of acrylates, optionally with regular stirring (408).

Examples of Liquid Developers with UV-Curable Additives in the TonerParticles Example 1

The above-described UV1 developer was tested in a HP 5000 Press, thatwas equipped with a UV curing unit (Light Hammer, from Fusion),including a 6 inch, 480 W/inch D bulb and a paper transport unit, andprinted at a process speed of 1.2 m/sec.

Example 2

A similar developer was tested (hereinafter UV2), but the UV curableadditive was CN9006, a hexafunctional aliphatic urethane acrylateoligomer by Sartomer, and the photoinitator mixture was made of 90%isodecyl acrylate (mono-actylate by UCB) and 10% of 1:1 mixture of EPDand ITX (a photo-initiator and a co-initiator by UCB). EPD isEthyl-4-(dimethylamino) benzoate, and ITX is Isopropyl thioxanthone.

In this experiment, the UV curing unit included a 6 inch, 480 W/inch Hlamp, providing the UV spectrum of Hg.

Results Obtained with the Developers of Examples 1 and 2

The abrasion resistance of images printed on three different papers wasmeasured (see below for details) and compared to that of images printedwith the same developer but without the UV-curable additive and withoutthe photoinitiator-mixture (hereinafter “reference”). The papers were:Condat-Gloss™ (an SBR (styrene butadiene rubber) coated paper), BVS (anacrylic coated paper), and Hadar-Top (a non-coated paper).

The results are presented in the following table. The figures in thetable represent the percentage of the damaged area.

Condat BVS HT paper paper paper Reference 30 48 27 UV1 22 25 20 UV2 2024 24

Example of UV-Curable Additives in the Carrier Liquid Example 3

8.33 g Ebecryl 1290 (hexa-functional urethane acrylate by UCB) are addedto 83.33 g DPDGA (Dipropylene Glycol Diacrylate by UCB) mixed with amagnetic stirrer for half an hour, at 50° C. and maximum speed. TheEbecryl dissolves in the DPDGA.

91.66 g Isopar™-L and to 0.14 g of NPAL stabilizer are added and mixedat a high shear mixer (Kady mill or Ross Mill) at more than 6,000 rpmfor 2 minutes at Room temperature. Before the high shear mixing theparticles size of the high acrylate was measured to be around 400 nm,and after high shear mixing, around 0.66 nm. The sub-nanometric size wasmeasure with a Zeta™ nanosizer by Malvern.

Additional Isopar™-L is added to obtain a mixture with 2% acrylate(w/w), which is stirred with a magnetic stirrer for about 10-20 minutesat room temperature. The obtained liquid is single-phase, and nophase-separation is observed by the naked eye.

Optionally, a photoinitiator with or without a co-initiator, and astabilizer for stabilizing the UV formulation, are also added to themixture. The stabilizer is added to ensure that small amounts of freeradicals that may be produced due for, for instance, exposure to sunlight, would not cause the UV-curable additive to cure. The stabilizeris added to the toner particle in the grinding stage, and thephotoinitiator is added to the liquid carrier.

Results Obtained with the Developer of Example 3

A developer was prepared as in the reference developer of example 1above, but with ISOPAR-L that contained 2% acrylates, and prepared inthe dilution method described above.

The developer was tested in an HP 5000 Press equipped with in-line UVcuring unit as in example 1 above, with a D bulb, at printing (andcuring) rate of 1.2 m/s, with three kinds of paper: Condat-SBR coatedpaper; BVS (acrylic coated paper); and Hadar Top (uncoated paper); allsupplied by Margol, Israel.

The results obtained with the formulation of example 3 are reproduced inthe following table. The numbers represent damaged area out of totalarea, in percentages.

Condat gloss 170 BVS H

Flaking Peeling Flaking Peeling F

UV(a) 0.101 1.5 0.93 19.6 0.

Ref 1.4 3.4 5.6 37.4 0.

indicates data missing or illegible when filed

Results of abrasion resistance are provided in the following table:

Condat BVS Hadar-Top UV(a) 45.8 64.3 33.7 Ref 67.9 78.6 39.6

Testing Methods

Abrasion resistance was quantitatively defined by a test based on ASTM D5264-92 standard.

Peeling damage was quantitatively defined by the following test: animage having 100% coverage is printed on the paper, and a scotch-tape isadhered to it and attached with a standard weight that is rolled on itfor ten times. Then, the tape is removed manually, and the image isanalyzed for percentage of damaged (white) area.

Flaking damage was quantitatively defined by the following test: twoimages (each on a separate paper) having 200% coverage were attached oneto a table, and one to a side of a book. The book was moved against thetable for 50 times, with the two images one against the other. Then, thelower image, the is, the one attached to the table, is analyzed forpercentage of damaged (white) area.

Examples 4-5

Two other formulations were prepared similar to the one of example 3,with the following constituents:

Formulation (b): Ebecryl 1290: 7.14 g; Additols (which is a 1:1 mixtureof ITX and EPD, a photo-initiator and a co-initiator by UCB) 7.14 g;DPGDA 85.56 g; and stabilizer: 0.15 g.

Formulation (c): like formulation (b) but 7.14 g of the DPGDA werereplaced with the same weight of CN152 (an aliphatic acrylate oligomerby Sartomer).

The present invention has been described using non-limiting detaileddescriptions of embodiments thereof that are provided by way of exampleand are not intended to limit the scope of the invention. It should beunderstood that features and/or steps described with respect to oneembodiment may be used with other embodiments and that not allembodiments of the invention have all of the features and/or stepsdescribed with respect to one of the embodiments. Variations ofembodiments described will occur to persons of the art. Furthermore, theterms “comprise,” “include,” “have” and their conjugates, shall mean,when used in the disclosure and/or claims, “including but notnecessarily limited to.”

It is noted that some of the above described embodiments may describethe best mode contemplated by the inventors and therefore may includestructure, acts or details of structures and acts that may not beessential to the invention and which are described as examples.Structure and acts described herein are replaceable by equivalents,which perform the same function, even if the structure or acts aredifferent, as known in the art. Therefore, the scope of the invention islimited only by the elements and limitations as used in the claims.

1. A method for printing a substrate by liquid developer electrography,the method comprising: (a) developing a latent image with liquiddeveloper comprising toner particles dispersed in a carrier liquid, saidtoner particles comprising UV-curable additive; (b) transferring thedeveloped image to the substrate; (c) at least partially fixing theimage to the substrate; and (d) irradiating the at least partially fixedimage with UV radiation to cure the UV-curable additive.
 2. A method forprinting a substrate by liquid developer electrography, the methodcomprising: (a) developing a latent image with liquid developercomprising toner particles dispersed in a carrier liquid, said tonerparticles comprising as a UV-curable additive a substance selected from:a hexa-functional acrylate or a multi-functional polyester acrylate; (b)transferring the developed image to the substrate; and (c) irradiatingthe image with UV radiation to cure the UV-curable additive.
 3. A methodfor printing a substrate by liquid developer electrography, the methodcomprising: (a) developing a latent image with liquid developercomprising toner particles dispersed in a carrier liquid, said carrierliquid comprising a multi-functional acrylate as a UV-curable additive;(b) transferring the developed image to the substrate; and (c)irradiating the image with UV radiation to cure the UV-curable additive.4. A method according to claim 1 wherein said carrier liquid comprises aUV curable additive.
 5. A method according to claim 3, wherein said UVcurable additive in said carrier liquid has an evaporation ratesubstantially less than that of at least some other liquid components ofsaid carrier liquid and wherein after said developing and prior to saidirradiating a portion of said other liquid components is evaporated,such that the concentration of UV curable additive is increased by anamount such that UV irradiation is effective to cure the curableadditive.
 6. A method according to claim 2, wherein before irradiatingthe image in (c) the image is at least partially fixed and/or at leastpartly fused to the substrate.
 7. A method according to claim 1, whereinthe UV irradiating is carried out within 10 seconds of the transfer tothe substrate.
 8. A method according to claim 1, wherein the UV-curableadditive comprises a multi-functional acrylate.
 9. A method for makingtoner particles, the method comprising grinding together a mixturecomprising a thermoplastic resin swelled with an aliphatic liquid, apigment, and a UV-curable additive.
 10. A method according to claim 9,wherein the UV-curable additive comprises multi-functional acrylate. 11.A method of making a one-phase liquid carrier comprising a non-polarliquid and a multi-functional acrylate, the method comprising: (a)mixing the multi-functional acrylate with acrylates of lowerfunctionality to obtain an acrylate mixture, and (b) diluting theobtained mixture with the non-polar liquid.
 12. A method according toclaim 2, wherein the multi-functional acrylate is tetra-functional,penta-functional, or hexa-functional.
 13. A method according to claim12, wherein the multi-functional acrylate is hexa-functional.
 14. Amethod according to claim 2, wherein the multi-functional acrylate is apolyester acrylate.
 15. A method according to claim 2, wherein themulti-functional acrylate is a polyurethane acrylate.
 16. A one phaseliquid carrier suitable for use as a carrier liquid for liquiddevelopers, comprising multi-functional acrylates.
 17. A one phaseliquid carrier according to claim 16, further comprising acrylates oflower functionality.
 18. A one phase liquid carrier according to claim17, wherein the multi-functional acrylates together with the acrylatesof lower functionality form from 0.5% to 5% of the liquid carrier, byweight.
 19. A one phase liquid carrier according to claim 17, whereinthe ratio between multi-functional acrylates and acrylates of lowerfunctionality is from 1:5 to 1:20, by weight.
 20. A one phase liquidcarrier according to claim 16, wherein the multi-functional acrylate isa polyurethane acrylate.
 21. A one phase liquid carrier according toclaim 16, wherein the multi-functional acrylate is a hexa-functionalacrylate.
 22. A one phase liquid carrier according to claim 17, whereinthe acrylates of lower functionality are bi-functional acrylates.
 23. Aliquid developer comprising toner particles dispersed in a liquidcarrier, the liquid carrier being according to claim
 16. 24. A liquiddeveloper comprising toner particles dispersed in a liquid carrier,wherein the toner particles include a thermoplastic resin, a pigment,and a UV-curable additive selected from: a hexa-functional acrylate, amulti-functional polyurethane acrylate or a multi-functional polyesteracrylate.
 25. A liquid developer according to claim 24, wherein theUV-curable additive comprises a polyester acrylate.
 26. A liquiddeveloper according to claim 24, wherein the UV-curable additivecomprises a hexa-functional acrylate.
 27. A liquid developer accordingto claim 24, wherein the liquid carrier comprises photo-initiators andan acrylate of lower functionality.
 28. A liquid developer according toclaim 27, wherein the acrylate of lower functionality has at roomtemperature a viscosity of up to 30 cps.
 29. A liquid developeraccording to claim 24, wherein the toner particles are tentacular.
 30. Aliquid developer according to claim 24 wherein the liquid carrier is aone-phase liquid carrier according to claim 17.